Product instability

G. W. Mushmsh and J. G. Speight, Petroleum Products Instability and Incompatibility, Taylor Francis, Washington, D.C., 1995. 

A related term is flame speed. Flame speed is the speed with which a flame appears to move relative to a stationary observer. The flame speed can be much larger than the burning velocity due to expansion ofthe combustion products, instability and turbulent deformation ofthe flame. Flame speeds of 30-300 ft/sec (9-90 m/sec) are commonly observed for hydrocarbon-air mixtures. A gas phase detonation occurs when the flame speed exceeds the speed of sound in the burning vapor air mixture. 

The use of desiccated thyroid rather than synthetic preparations is never justified, since the disadvantages of protein antigenicity, product instability, variable hormone concentrations, and difficulty in laboratory monitoring far outweigh the advantage of low cost. Significant amounts of T3 found in some thyroid extracts and liotrix may produce significant elevations in T3 levels and toxicity. Equivalent doses are 100 mg (1.5 g) of desiccated thyroid, 100 Mg of levothyroxine, and 37.5 ug of liothyronine. 

As mentioned above, one other big lever is to optimize product and information flows, taking a cross-functional view of the entire supply chain from the original supplier to the end customer. This can reduce inventory levels substantially, as well as smoothing out production instability and its associated costs. It also often helps to improve levels of customer service, such as on-time delivery, and capacity utilization. 

The future reduction in PEM fuel cell prices is indicated in Fig. 6.1 in terms of two curves corresponding to learning rates of 10-20% corresponding to the limiting cases of photovoltaic modules and wind turbines over the recent decade. Even with the lower curve, break-even with current vehicles would not be reached until the cumulated production reached about 500 GW. However, difficulties with the market for oil products (peaking production, instability of major supplier countries) may make PEM fuel cell vehicles competitive at higher prices than the currently seen break-even price. 

The development of a successful tablet formulation can be a substantial challenge, because formulation scientists are often confronted with a bewildering array of formulation and process variables that can interact in complex ways. These interactions will primarily be discussed in Volume 2, but to understand these interactions the reader must first have a good understanding of the different unit operations involved in making a tablet, the physicochemical and mechanical properties of the active drug substance, and the causes of drug product instability. 

Other unsymmetrical diols, prepared (inefficiently) by the coupling of mixtures of ketones, have been studied. The preferred cation argument is also found to be applicable to mixed medium-ring analogs, i.e. the kinetically favored pinacol rearrangement product is that predicted by consideration of the relative stabilities of the two possible, initially formed, carbocations. ° Earlier work with these compounds may have given misleading results due to product instability. To illustrate, Mundy observed that (24) is converted to (25) as the temperature is increased. 

A striking example of enhanced reactivity is found in the vitamin A related studies of Rosenberger et al. The example shown (equation 98) and several other analogous high yield reactions almost certainly proceed via the stabilized carbocation (tertiary and dienyl in this instance). Higher temperatures were detrimental to these applications, probably because of product instability. 

Certain issues of product instability may be resolved by formulation or careful selection of vehicle. Aminophylline injection, for example, is a solution of the drug in Water for Injections free from carbon dioxide, as the presence of this gas causes precipitation of the active. Similarly, promethazine injection is a solution of the active in Water for Injections free from dissolved air as the presence of oxygen would cause promethazine oxidation. Removal of these gases can be accomplished by prior boiling additionally the product may be packed under an atmosphere of nitrogen to eliminate oxygen from the head space in the ampoule. 

Calcium carbonate does not have functional groups (its surface is inert), therefore interaction can only be improved by chemical modification. Some hydroxyl groups can be found from admixtures such as Ca(OH)2 but these admixtures may limit the ways in which calcium carbonate can be used because these admixtures increase the amount of absorbed moisture. Functional groups are frequently hydrophilic thus they attract water molecules. In many applications, moisture can either cause product instability, reduce cure rate, or reduce reinforcement. Caution is needed in selecting surface treatment to generate functional groups. 

Care should be taken in the selection of preservative systems to avoid interaction between preservatives and ingredients or packaging material that could inactivate the preservative, cause product instability, or irritation to skin [101]. 

The particle size distribution of the dispersion depends on the magnitude of the shear and of the flow applied at each step of the formulation. The wrong conditions may induce two kinds of product instability thickening or clearing upon storage. 

The reactions are catalyzed by tertiary amines, quaternary ammonium salts, metal salts, and basic ion-exchange resins. The products are difficult to purify and generally contain low concentrations of acrylic acid and some diester which should be kept to a minimum since its presence leads to product instability and to polymer cross-linking. 

Durst has shown that a Diels-Alder adduct is in fact the kinetic product of reactions of sulfur dioxide with conjugated dienes, but is thermally unstable and readily undergoes a retro-Diels-Alder reaction to butadiene and sulfur dioxide. A thermodynamically more favorable addition then ensues, producing a stable five-membered ring adduct. Thus, the apparent inability of sulfur dioxide to form Diels-Alder adducts is not one of reactivity, but of product instability. 

The effect of additives. Here the aim was to attempt to trap out any reactive boron species that may have been causing the product instability. The addition of various aldehydes, or dienes, boron specific ion exchange resins or other boron trapping agents just before work-up had no effect on the product stability. 

The observed yields in entries 2 and 3 are still a result of the product instability to reagent excesses and work-up conditions. Entries 5 and 6 indicate that when the enolate excess falls below a certain value, the reaction is very slow and incomplete conversion is observed. Entry 8 shows the remarkable effect of water. Here the (+)-DlP-Cl was exposed to atmospheric moisture for one to two seconds simply by removing the stopper of the weighing flask. No aldol product was formed and a 1/1 mixture of 8 and its isomer 54 was observed. The conditions of entry 4 are apparently optimal. However, the reaction is very intolerant of manipulative errors and very narrow limits between stow reaction and product stability are apparent. These conditions brought a benefit. The crude product was found to be stable indefinitely to the reagents and the work-up system. Stability tests of 64a showed no loss in yield even when the mixture was kept at 40 °C. 

The kinetic order of both E2 and 8 2 reactions requires that during the course of the reaction, the product ratio remains constant. Any deviation from this behavior indicates a departure from kinetic control due to product instability under the reaction conditions or more frequently, the incursion of competing... 

Enzymes are highly desirable catalysts when the specificity of the reaction is a major issue (as it occurs in pharmaceutical products and fine chemicals), when the catalysts must be active under mild conditions (because of substrate and/or product instability or to avoid unwanted side-reactions, as it occurs in several reactions of organic synthesis), when environmental restrictions are stringent (which is now a... 

Yields are variable, mainly due to product instability (Scheme 7). Conditions for the mono-o-methylation of. 3,Y -unsaturated acids have also been. established during, a detai.led study. 

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